The invention concerns a finger joint prosthesis comprising a joint body having first and second joint elements. The joint elements are connected together pivotably about a rotary axis, and extending from each joint element is an elongate anchoring bar for fixing to a proximal and/or distal phalanx. One or more eyes with openings for receiving fixing screws are also provided on the anchoring bars.
Functional troubles with finger middle joints can occur on the one hand by virtue of genetic degenerative disease, joint arthrosis. In that case, the disease leads to “wear” of the joint cartilage and consequently corresponding inappropriate strains and pressures with complete changes in the joint surfaces, which result in painful restriction on or even elimination of the joint function. On the other hand, functional troubles with the finger middle joints can, however, also occur as a result of an injury, for example due to luxation of the joint or due to a joint fracture. Primary treatment of a joint fracture generally results in what is referred to as “post-traumatic arthrosis” of the joint, which also leads to a painful restriction in function or elimination of function of the finger middle joint.
One way of eliminating the above-indicated functional problems is to stiffen the joint in a position which is convenient for function thereof. That procedure admittedly results in freedom from pain, but it signifies complete functional inoperability of the joint.
For the implantation of earlier finger joint prostheses, the internal lateral ligament at the finger joint had to be released for ulnar access. The joint was then luxated laterally and a part of the palmar plate detached. The head of the first phalanx and the base of the second phalanx were then resized, so that a previously agreed spacing was afforded between the two phalanges. Thereupon a rectangular space extending along a central axis was reamed by a rasp in each phalanx. A shaft, guide was cemented into that rectangular space. The joint elements were then individually fitted with their anchoring bars into the shaft guide, the phalanges were bent back, and the first and second joint elements were hingedly connected together by inserting a spindle into the aligned openings.
As the finger middle joint had to be luxated laterally in the procedure for implantation of the known finger joint prostheses, the extensor tendon system, the two flexor tendons and the lateral ligaments of the joint were irritated, which resulted in operability being later adversely affected. In addition a large amount of bone substance was sacrificed for implantation of the finger joint prosthesis, as a shaft guide had to be inserted in the direction of the central axis of the finger joints.
A markedly improved finger joint prosthesis is known from European Patent EP 1 096 906 to the inventor Christoph Ranft. That permits a novel and improved method while avoiding the above-indicated disadvantages. In the method described in EP 1 096 906 the finger joint prosthesis could be implanted in the assembled condition radially into a previously produced bore in the finger joint, which represents a marked simplification in installation and results in slight injuries to the finger.
On the other hand, that finger joint prosthesis is of an excessively filigree structure and suffers from a lack of strength and durability.